Preparation of olefins



United States Patent Ofi tice 3,278,619 Patented Oct. 11, 1966 3,278,619 PREPARATION OF OLEFINS Herman S. Bloch, Skokie, 11]., assignor to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware No Drawing. Filed Sept. 30, 1965, Ser. No. 491,879 12 Claims. (Cl. 260-666) This application is a continuation-in-part of a copending application Serial No. 270,543, filed April 4, 1963, now abandoned. I

This invention relates to the preparation of olefinic hydrocarbons. More particularly, this invention relates to a novel method of preparing olefinic hydrocarbons from saturated hydrocarbons.

The preparation of olefinic hydrocarbons by the thermal and/or catalytic dehydrogenation of saturated hydrocarbons is a highly endothermic process. In many cases the required temperatures lead to undesirable side reactions, poor product distribution and carbon formation. For example, straight chain monoolefins in the C -C range are important alkylating agents in the manufacture of certain straight chain alkylbenzenes, the sulfonated derivatives of which are desirable biodegradable detergents. Straight chain hydrocarbons in the aforesaid range are particularly susceptible to thermal and/ or catalytic cracking and cyclization at dehydrogenation temperatures and the yield of desired C -C monoolefins is considerably reduced.

It is therefore an object of this invention to present a novel method of preparing olefinic hydrocarbons, which method can be effected at comparatively moderate temperature conditions.

In one of its broad aspects, the present invention embodies a method of preparing a monoolefinic hydrocarbon which comprises reacting a saturated hydrocarbon at a temperature of from about 200 C to about 600 C with a dehydrogenating agent consisting essentially of a saturated polyhalohydrocarbon containing at least two halogen atoms attached to the same carbon atom and converting said saturated hydrocarbon to a monoolefinic hydrocarbon of the same carbon configuration.

Another and more specific embodiment of the present invention is in a method of preparing a monoolefinic hydrocarbon which comprises reacting a saturated hydrocarbon at a temperature of from about 200 C. to about 600 C. with a dehydrogenating agent consisting essentially of carbon tetrachloride and converting said saturated hydrocarbon to a monoolefinic hydrocarbon of the same carbon configuration.

Still another embodiment of the method of this invention relates to the preparation of a monoolefinic hydrocarbon and comprises reacting a saturated hydrocarbon at a temperature of from about 200 C. to about 600 C. with a dehydrogenating agent consisting essentially of chloroform and converting said saturated hydrocarbon to a monoolefinic hydrocarbon of-the same carbon configuration.

Further objects and embodiments of the present invention will become apparent in the following detailed specification.

In accordance with the method of this invention, a saturated hydrocarbon is reacted with a saturated polyhalohydrocarbon. The saturated polyhalohydrocarbon, utilized herein as a dehydrogenation agent, should contain at least two halogen atoms attached to the same carbon atom. Suitable saturated polyhalohydrocarbons thus include polychloro derivatives of saturated hydrocarbons, for example, methylene chloride, chloroform, carbon tetrachloride, 1,1-dichloroethane, 1,1,1,-trichloroethane, 1,1,2-trichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, hexachloroethane, 1,1-dich1oro-propane, 2,2-dichloropropane, etc., and also polychloro derivatives of cyclic saturated hydrocarbons like 1,l-dichlorocyclohexane, 1,1-dichlorocyclopentane, and the like. Of the above-mentioned types, the substituted methanes are preferred, since they undergo minimal side reactions. The corresponding bromo, fluoro, and iodo derivatives of saturated hydrocarbons are also operable, although the chloro derivatives are preferred because of greater economy of operation. Saturated p-olyhalohydrocarbons comprising different halogen atoms as in the case of trifluorochloromethane, dichlorodiflu-oromethane, trichlorofluoromethane, dichlorofluoromethane, difiuorochlorobr-omomethane, dichlorodibromomethane, trifluorobromomethane, difluorobromomethane, difluorochlorobromomethane, 1,1-dichloro- 1,2,2,2-tetrafluoroethane, 1,1,1,2-tetrachloro-2,2-diflu-oroethane, 1,1,1-trichloro-2,2,2-trifluoroethane, l-chloro- 1,1,2,2,2-pentafluoroethane, and the like, are also operable and Within the scope of this invention.

The saturated hydrocarbons utilized in accordance with the method of this invention may contain up to about 20 carbon atoms or more. The saturated hydrocarbons, which can be aliphatic or cyclic, should contain at least one hydrogen atom attached to each of two adjacent carbon atoms. At the conditions herein described, the saturated hydrocarbon starting material is converted principally to monoolefinic hydrocarbons which are of the same carbon configuration as the starting material. Thus, heptane is converted to a mixture of heptenes, isobutane is converted to isobutene, and cyclohexane is converted to cyclohexene. Although ethane is operable as a saturated hydrocarbon, its rate of reaction is substantially slower than its higher homologs and the saturated hydrocarbons preferably contain more than two carbon atoms. Saturated hydrocarbons which can be utilized thus include cyclopentane, methylcyclopentane, cycl-ohexane, methyl-cyclohexane, and the like, and also propane, butane, isobutane, pentane, isopentane, hexane, etc., and higher homologs and structural isomers thereof containing up to about 20 carbon atoms or more for example, heptane, decane, pentadecane, eic-osane, and the like.

Reaction conditions relate principally to temperature. Pressure does not appear to be an important variable with respect to the method of this invention and may be atmospheric, or the autogenous pressure developed during the course of the reaction, or it may be an imposed pressure to facilitate a process flow. reacting a saturated hydrocarbon with a saturated polyhalohydrocarbon at a temperature of from about 200 C. to about 600 C. will efiect the conversion of said saturated hydrocarbons primarily to a monoolefinic hydrocarbon as herein contemplated. F-ormation of polyunsaturated by-products, such as diolefins and aromatics, is favored by more severe react-ion conditions including extended contact times, temperatures in the higher range and in excess of about 600 C., and also higher ratios of halohydrocarbon to hydrocarbon in the reaction mixture. It is preferred to utilize a temperature of from about 300 C. to about 500 C., the optimum temperature in any particular case being in part dependent upon the hydrocarbon being treated and the halohydrocarbon employed, and in part upon the contact time of the reactants.

The method of this invention is preferably carried out in a continuous type of operation. For example, the starting materials, comprising a saturated hydrocarbon and a saturated polyhalohydrocarbon, are continuously charged In general,

through a reactor maintained at the prescribed temperature and at a suitable pressure. The saturated hydrocarbon is preferably charged with the polyhalohydrocarbon in at least an equimolar amount, preferably in a ratio of about 1 to about moles of saturated hydrocarbon per mole of polyhalohydrocarbon. The reactants may be combined and charged to the reactor in a single stream or introduced thereto in individual streams. The reactor can be an unpacked vessel or coil, or it may contain an inert packing such as glass chips or beads, or an absorbent packing material such as fire brick, alumina, dehydrated bauxite, and the like. The reactor effluent is withdrawn at a rate which will insure an adequate residence time therein. A residence time of from about 0.5 hour to about 5 hours is suitable, the more extended periods being utilized in the case of a once-through operation. The reactor eflluent is collected in a separator maintained at substantially the same pressure as the reactor and at a reduced temperature to effect separation of the gaseous hydrogen halide and other gaseous products formed during the reaction. The residual eflluent is withdrawn from the separator, caustic scrubbed and fractionated. The olefinic hydrocarbon product is recovered and the unreacted starting materials recycled to form a portion of the feed stock.

The following examples are presented in further illustration of the method of this invention. It is not intended that said examples shall serve as an undue limitation on the generally broad scope of this invention as set out in the appended claims.

Example I In a once-through operation a liquid charge stock comprising equimolar amounts of cyclohexane and carbon tetrachloride is charged to a vertical tubular reactor of about 500 cubic centimeters capacity packed with glass beads. The liquid charge stock is charged at a rate of about 100 cubic centimeters per hour while maintaining the reactor pressure at about 50 p.s.i.g. and the reactor temperature at 400450 C. The reactor efiluent is cooled to about room temperature and hydrogen chloride separated therefrom. The liquid product is recovered, washed with dilute alkali, dried and distilled. A chloroform fraction and a higher boiling carbon tetrachloride fraction are separated. A cyclohexene-cyclo-hexane fraction comprising about cyclohexene is recovered as higher boiling material, a portion of the unconverted cyclohexane being recovered also in the carbon tetrachloride fraction. The cyclohexene-cylohexane fraction further contains small amounts of cyclohexadiene and benzene.

Exampl II n-Heptene is prepared by heating n-heptane with trifluorobromomethane at a temperature of about 350 C. The n-heptane and the halide are charged to a reactor substantially as described in Example I. The 'n-heptane and the mixed carbon tetrahalide are charged as an equimolar solution of the same and at a rate of about 100 cubic centimeters per hour. The reactor temperature is maintained at about 350 C. and the reactor pressure at about 5 p.s.i.g. The reactor effluent is cooled to room temperature and gaseous hydrogen bromide, fluoroform and unreacted trifiuorobromomethane separated therefrom. The liquid product is washed with dilute alkali, dried and analyzed by gas-liquid chromatography. It is found to contain a major amount of unconverted nheptane, about 15% of n-heptenes, small amounts of heptadienes, and traces of toluene.

Example III In the preparation of isobutene, isobutane and carbon tetrachloride are charged to the above-described reactor in a mole ratio of about 1:1 and at a rate of about 200 cubic centimeters per hour The reactor temperature is maintained at about 325 C. and the pressure at about 60 p.s.i.g. The reactor efiluent is quickly cooled to about room temperature and the gaseous portion thereof recovered through a series of caustic scrubbers. The gaseous product thus treated comprises in excess of 50% of the theoretical yield of isobutene, together with unreacted isobutane, chloroform, and small amounts of carbon tetrachloride.

Example 1V Carbon tetrabromide is heated with n-dodecane at a temperat re of about 375400 C. to prepare n-dodecene. The reactants are combined in about equimolar amounts and charged to a reactor substantially as described at a rate of about cubic centimeters per hour. The reactor is heated at the aforesaid temperature and the pressure is maintained at about 5 p.s.i.g. The reactor efiluent is cooled to room temperature and hydrogen bromide separated therefrom. The liquid product is washed with dilute alkali, dried and distilled. After removal of bromoform and unreacted carbon tetrabromide, the hydrocarbon fraction is found to contain 22% of n-dodecenes and small amounts of dienes as well as a major amount of unreacted dodecane.

I claim as my invention:

1. A method of preparing an olefinic hydrocarbon which comprises heating at a temperature of from about 200 C. to about 600 C. a reaction mixture consisting essentially of a saturated hydrocarbon in at least an equimolar amount with a saturated polyhalohydrocarbon having at least two halogen atoms attached to the same carbon atom to convert a substantial portion, at least, of said saturated hydrocarbon to a monoolefinic hydrocarbon of the same carbon configuration as the saturated hydrocar-bon and form hydrogen halide, and separating said mono-olefinic hydrocarbon from the hydrogen halide.

2. The method of claim 1 further characterized in that said reaction mixture contains said saturated hydrocarbon and said polyhalohydrocarbon in approximately equimolar amounts.

3. The method of claim 1 further characterized in that the halogen of said polyhalohydrocarbon is chlorine.

4. The method of claim 1 further characterized in that said polyhalohydrocarbon is carbon tetrachloride.

5. The method of claim 1 further characterized in that said polyhalodhydrocarbon is carbon tetrabromide.

6. The method of claim 1 further characterized in that said polyhalohydrocarbon is chloroform.

7. The method of claim 1 further characterized in that said reaction mixture consists essentially of cyclohexane and carbon tetrachloride.

8. The method of claim 1 further characterized in that said reaction mixture consists essentially of ndodecane and carbon tetrabromide.

9. The method of claim 1 further characterized in that said reaction mixture consists essentially of isobutane and carbon tetrachloride.

10. The method of claim 1 further characterized in that said reaction mixture consists essentially of n-heptane and trifluorobromomethane.

11. The method of claim 1 further characterized in that said saturated hydrocarbon is an aliphatic hydrocarbon.

12. The method of claim 1 further characterized in that said saturated hydrocarbon is a cyclic hydrocarbon.

References Cited by the Examiner UNITED STATES PATENTS 2,416,660 2/1947 Folkins 260-683 2,890,253 6/1959 Mullineaux 260-680 3,116,338 12/1963 Guest 260666 DELBERT E. GANTZ, Primary Examiner.

V. O. KEEFE, Assistant Examiner. 

1. A METHOD OF PREPARING AN OLEFINIC HYDROCARBON WHICH COMPRISES HEATING AT A TEMPERATURE OF FROM ABOUT 200*C. TO ABOUT 600*C. A REACTION MIXTURE CONSISTING ESSENTIALLY OF A SATURATED HYDROCARBON IN AT LEAST AN EQUIMOLAR AMOUNT WITH A SATURATED POLYHALOHYDROCARBON HAVING AT LEAST TWO HALOGEN ATOMS ATTACHED TO THE SAME CARBON ATOM TO CONVERT A SUBSTANTIAL PORTION, AT LEAST, OF SAID SATURATED HYDROCARBON TO A MONOOLEFINIC HYDROCARBON OF THE SAME CARBON CONFIGURATION AS THE SATURATED HYDROCARBON AND FORM HYDROGEN HALIDE, AND SEPARATING SAID MONO-OLEFINIC HYDROCARBON FROM THE HYDROGEN HALIDE. 